Chemistry Reference
In-Depth Information
Organiccomplexesusedascytostaticagentscanbedistinguishedby
XANES
. Platinum complexes, such as cis- and carbo-platinum inhibit cell
growth and are used as strong chemotherapeutic substances; however, they
have unpleasant or even toxic side effects. In order to develop new antitumor
drugs, platinum was replaced by platinoids, such as ruthenium, rhodium, and
rhenium [139]. Human cancer cell lines treated with a highly active rhodium
agent were investigated by XANES in fluorescence mode. At grazing inci-
dence, the excitation energy was shifted across the K edge of Rh (23.220 keV)
and different types of rhodium species were detected in the spectrum. They
could be distinguished by comparing spectra of different rhodium complexes
as fingerprints. Complexes similar to RhCl
3
were shown to be the most
effective cytostatic agents.
CryosectionsofbraintissuecanbecharacterizedbyTXRFandXANESwith
μ
mlocalresolution
. Samples were cut from tumor tissue or Parkinson's-
affected tissue of a human brain during autopsy [140]. The tissue samples
were cryosectioned to a thickness of 5-20
μ
m and the sections were placed and
stretched on polymer discs. TXRF as well as XANES were carried out with
synchrotron excitation, while 2D mapping was made possible by focusing the
monochromatized beam with polycapillary lenses or Kirkpatrick-Baez mirrors
to a diameter of 15
μ
m. Particular elements, such as Cl, Fe, Ca, and Zn, with
high levels of concentration can be used for a general discrimination of
malignancy. Different oxidation states between 1
+
and 3
+
of iron, copper,
and zinc in tissues were determined. It could be shown that the distance of
atoms within the first coordination zone from a central atom is correlated with
the grade of malignancy.
ChemicalspeciationbyXANESorNEXAFSisalsopossibleingrazingexit
geometryasshownbyMeireretal
. [141]. It was tested for the analysis of arsenic
traces in water droplets and compared with grazing incidence geometry. The
combination of XANES with grazing exit geometry showed distinct oscillations
above the K edge of arsenic at 11.867 keV. They were not damped or smeared
out as was the case for the combination with grazing incident geometry. Due to
a short path length of the primary beam, GE-XRF hardly suffered from self-
absorption effects in concentrated samples (
>
20 ng arsenic/
μ
l). Furthermore,
the sample could be excited by a focused microbeam of 40
μ
m spot size, and
area maps of 1200
×
1000
μ
m
2
became possible. However, GE-XRF is much less
sensitive for traces (factor 1/30) so that small amounts of arsenic (
<
4 ng arsenic/
μ
l)
could only be characterized by XANES with grazing incidence geometry.
7.3.4X-rayDiffractometryatTotalReflection
X-ray diffraction analysis is a method parallel to the wavelength dispersive
mode of X-ray fluorescence and both methods are based on Bragg's reflection
(see Section 1.5.2). For wavelength-dispersive spectrometry, the sample
excited by X-rays emits X-rays that are reflected at an analyzer crystal under
a certain reflection angle. The relevant interplanar spacing of the analyzer
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